Update virt installation to not require root for VMs

[leifmadsen]

I've set this up previously, but it's usually done from looking through a bunch of different blogs and documentation locations. I found this today, which documents how to set it all up in a single space.

http://ixday.github.io/post/unprivileged_libvirt/

We should avoid the use of running as root if we can avoid it. As part of the future migration to kvm-inventory-builder we could adjust the plays so that they run as non-root.